Epididymal fat is necessary for spermatogenesis, but not testosterone production or copulatory behavior

Surgical removal of the epididymal white adipose tissue (EWAT) depot (lipectomy; EWATx) in laboratory rats or mice decreases spermatogenesis, but this phenomenal finding has not been investigated in depth. Specifically, detailed histology, neuroendocrine profiles, copulatory behavior, lipectomy of other WAT depots, rescue by autologous EWAT transplants, or tests whether this EWATx effect is due to disruption of testes innervation occurring during EWATx have not been performed. Therefore, in the first study, we performed EWATx in male Syrian hamsters and attempted to rescue spermatogenesis by transplanting the removed EWAT to the animal's subcutaneous dorsum, removed comparable or larger amounts of non-gonadal WAT [inguinal WAT (IWAT)] and conducted mating behavior tests. In a second study we conducted detailed testicular histology and assayed serum LH, FSH, and testosterone (T). In a third study, we surgically denervated the testes without removing EWAT and compared testicular histology with that of EWATx or sham surgery. We found that EWATx, but not IWATx, virtually eliminated spermatogenesis producing a marked decrease in size of the seminiferous tubule cellular lining including the Sertoli cells and spermatogonia that could not be rescued by autologous EWAT transplant to the subcutaneous dorsum. EWATx did not change serum LH or T concentrations but approximately doubled serum FSH concentrations. EWATx did not alter copulatory behavior but resulted in aspermatic ejaculate. Selective surgical testicular denervation did not affect spermatogenesis. Collectively, these results suggest the presence of a local, but currently unidentified, growth and/or nutritive factor from EWAT that promotes spermatogenesis.